1. Field of the Invention
The preset invention relates to a combined system including a machine tool and a robot.
2. Description of the Related Art
In a production line including a machine tool such as a machining center or a lathe, a robot is often used to carry out an exchange operation of a workpiece or a tooling, etc. An installation environment of the machine tool and the robot may be different between each production line. For example, the machine tool and the robot are independently located on a floor, or, the robot may be mounted on the machine tool located on the floor.
When a pedestal of the machine tool or the robot is fixed to the floor, it is preferable that the pedestal be tightly fixed by using an anchor bolt, etc. On the other hand, when the machine tool or the robot cannot be fixed or is loosely fixed to the floor, the install position thereof relative to the floor may be displaced due to vibration generated by the motion of the machine tool or the robot. As a result, the positional relationship between the robot and the machine tool may be changed.
Normally, the robot is moved along positional coordinates which are previously taught based on the positional relationship between the machine tool and the robot, so as to carry out the exchange operation of the workpiece, etc. Therefore, when the positional relationship between the machine tool and the robot is changed, a jig of the machine tool may interfere with the workpiece during the exchange of operation of the workpiece, whereby a load of each axis of the robot may be increased and/or the posture of the workpiece when attaching it to the jig may be changed. As a result, the workpiece cannot be correctly exchanged in the machine tool.
In such a case, it is necessary to teach the robot again. In particular, in a system where one robot is operated so as to attach/detach a workpiece for a plurality of machine tools, it is necessary to teach the robot for each machine tool when the position of the robot relative to the floor is displaced.
As a relevant prior art for automatically teaching a robot in a short time, JP H05-111886 A discloses a robot system in which a six-axes for sensor is attached to a manipulator so as to carry out impedance control of the manipulator, and a calibration method in which fix-point observation is carried out by inserting a tool (rod) attached to a wrist of the manipulator into a hole of the jig.
JP 2013-006244 A discloses a position adjustment method, in which a motion for exchanging a work tool based on a previously determined command value is executed, and the command value is corrected, based on the magnitude and direction of a load generated by interference between the work tool and a robot during the exchanging motion, so as to reduce the load.
JP 2009-208209 A discloses a technique in which an amount of deviation of the position of a first work table from a predetermined position is detected by a camera, so as to correct teaching data used as criteria for the motion of a conveyor robot, based on the detection result.
Further, JP H05-116094 A discloses an abnormal load detection method, in which a disturbance torque estimated by a disturbance observer immediately before a movable part of a machine is stored, the stored disturbance torque is subtracted from an estimated disturbance torque during the movable part is moved, and the calculated value is detected as an abnormal load when the calculated value is larger than a setting value.
In the technique of JP H05-111886 A, JP 2013-006244 A or JP 2009-208209 A, a dedicated detection unit is used to obtain information regarding the positional misalignment. Therefore, when the detection unit is attached to the manipulator, the weight of the workpiece handled by the manipulator is limited due to the weight of the detection unit.
On the other hand, a disturbance value such as the estimated disturbance torque as described in JP H05-116094 A is varied depending on whether or not a robot interferes with and a workpiece, and thus it is possible to judge as to whether or not the interference occurs, based on the disturbance value of each axis. However, in general, when each axis of the robot is operated, the disturbance value of each axis is dynamically changed without depending on the occurrence of the interference, in particular, an amount of the change in the disturbance value is increased as the motion speed of the axis is increased. Therefore, in the method for judging the occurrence of the interference based on the disturbance value, it is necessary to significantly reduce the motion speed (or search speed) of the robot for avoiding the interference, in order to preventing false detection due to the change in the disturbance value. As a result, it is difficult to operate the robot so that the robot quickly moves in order to avoid the interference (or correct the positional misalignment).